Monitoring Bank With Analog Volt Meters

[ChrisOlson]

In late spring I installed dual analog meters to monitor the voltage on the two halves of our battery bank.  It looks like this:



We have 24 Rolls T12-250's, 24 volt system.  The batteries are arranged in parallel strings with 12 batteries in each string, and one series connection between the two strings to make 24 volts.  This was a new arrangement at the time to help alleviate problems with too many series connections causing batteries to get out of whack.

In July, when we had 100 degree heat day after day, plus day after day of bright sunny weather, the bank went thru a lot of water.  I didn't get clued in to this fact until I noticed my analog meters weren't the same by about a needle's width one day.  That wasn't normal, from what I had seen over the three months it had operated that way.  So I checked the bank and found all the batteries low on water and one battery that was probably low the last time I serviced them had boiled itself down to where the top of the plates were exposed to the air, and that battery had super high at-rest voltage because it was going dry.  I watered the bank and it took over 5 gallons of water.

My Classics are set up to equalize at 32.0 volts, absorb at 30.0 and float at 27.0.  All those voltages are temp compensated.  The equalize is set up so it's done automatically every 30 days for 30 minutes by the Classic 150 on the solar array, and the wind turbines help out.  Slightly after noon today I noticed that the two meters were well over 15 and it was doing its monthly 30 minute equalize job.

So I waited until it got done and dropped into float.  Then I started the generator, flipped the transfer switch to take the loads off the inverters and batteries and let the batteries rest for an hour.  I decided this would be a good chance to service the whole bank because with fall coming I got wood to make, fishing and hunting to do, and crops to harvest - don't have time to mess around with batteries.

When I service the batteries I check the water, record the at-rest voltage, load each one for one minute at 50 amps and record the loaded voltage, then let it recover for one minute and record the at-rest voltage after being load tested.  Every battery in the bank tested with the same specs as new.  The batteries are going into their third winter.

So even though some folks told me the analog meters won't work and I should have digital, I'm still pretty happy about a couple things.  The meters do work.
1. They told me that I had a battery low on water and I caught it and corrected it before it got wrecked.
2. Arranging big 12 volt batteries in large parallel strings with only one series connection works.
--
Chris

[Volvo farmer]

All I have to say is that I have never heard of any experienced installer or dealer in the RE industry recommending a whole bunch of parallel strings.  You may prove the whole world wrong by doing it that way and making it work. Maybe you will get twelve years out of that bank and prove all the so called "experts" with decades of experience wrong. Maybe all the folks that said it is extremely easy for parallel batteries to get out of balance from each other and fool voltage-based charge controllers just didn't wire them up right and monitor them with analog meters.

I have a lot of respect for the things you can do with wind turbines, and your knowledge of farming and skill at fabricating towers, but I think you are dead wrong about preferring parallel to series strings for lead acid batteries in off-grid applications.

I just did the opposite. I got one series string of big old 2V cells at 24V in the neighborhood of 800 Ahr.  It wasn't cheap, but I believe the fewer parallel strings, the better. Maybe we'll meet back here in five or six years and I'll eat my words, but every single piece of data I have ever found on this subject backs up my assertations.

[Watt]

Chris:
You said going on third winter but one of the posted thread reads as the batteries are new as of ( April 2011 ).

Volvo Farmer:
As far as his meters go, I gotta admit I like them and believe me I've been watching close.  He was able to tell when a battery was showing troubles.  I really don't know why meters like this or digital, can't be used no matter the configuration and the meters are very handy for the at a glance view as he wanted.  Also, his need for lots of current and that current being available while keeping his bus voltage as high as possible, is why I believe he does more parallel connections than series.  However, not seeing the connection scheme, I can only assume based on his comments. 

~

There really is more to this story.  http://www.anotherpower.com/board/index.php?topic=513.0

My particular concern was the wiring which was done to the entire bank using the first post and number 21 post download as reference.  It was clear that configuration would show signs of trouble and If I remember right, the meters showed problems with that connection.  ( not sure though )
 
I'm not exactly sure how he has his bank wired so.....  No way for me to tell exactly what's going on battery to battery.

Here is another thread http://www.anotherpower.com/board/index.php/topic,224.0.html which shows some history. 

 

[boB]

 Batteries in parallel at least have the same voltage across them.  As long as the wiring is such that they can be discharged with equal current, (positive on one corner and negative connected to the kitty-corner), they should balance pretty well.

Multiple batteries in series is pretty hard to keep in balance especially if the string is tapped for lower voltage loads.

Of course, the more batteries in series or parallel will have a higher chance of unbalancing in either case.  Installers usually
don't like to have too many strings in parallel but will use single larger cells with lower voltage  like 2V L-16s.

A "battery balancer" would be a neat product.  These are used all the time with Lithium strings because it is a BIG issue if they get out of balance.

boB

[Watt]

boB, could you touch a little more on these comments.  I do understand the " lower voltage tap " issue.

"Multiple batteries in series is pretty hard to keep in balance especially if the string is tapped for lower voltage loads."

" A "battery balancer" would be a neat product.  "


 

[boB]

What I mean by tapping the string of batteries is that with a battery bank for 24 or 48 volts for example, the user may
have some 12V loads such as radios etc. that he wants to run off of that bank.

You do not want to just hook up a load to the first 12 volts of the string otherwise when charging, some
batteries will be full sooner than the other cells and can unbalance the voltages and damage things
pretty quickly.  I find that AGMs are worse than flooded lead acid batteries but they can all get
unbalanced.

Using a 24V or 48V to 12V converter from the full string of battery cells is  a good way to come up with the
12V.  Those converters already exist but may not have enough power for some loads.

A battery balanced ensures that voltage across all batteries are the same during charge and discharge.

If the balancer does not have enough capability to completely balance all cells during a heavy
unbalanced discharge, hopefully the balancer helps to balance during the charging process.
We have talked about building a balancer for many years now but it would have to be very
inexpensive to be a viable product.  There are some already out there I believe.  They're
not very powerful though as I remember.

boB

[Mary B]

Instead of tapping my 24 volt bank for the ham gear I went with a 24 to 12 volt converter. $100 well spent with less fussing with the batteries.

[Watt]

What I mean by tapping the string of batteries is that with a battery bank for 24 or 48 volts for example, the user may
have some 12V loads such as radios etc. that he wants to run off of that bank.

You do not want to just hook up a load to the first 12 volts of the string otherwise when charging, some
batteries will be full sooner than the other cells and can unbalance the voltages and damage things
pretty quickly.  I find that AGMs are worse than flooded lead acid batteries but they can all get
unbalanced.

Using a 24V or 48V to 12V converter from the full string of battery cells is  a good way to come up with the
12V.  Those converters already exist but may not have enough power for some loads.

A battery balanced ensures that voltage across all batteries are the same during charge and discharge.

If the balancer does not have enough capability to completely balance all cells during a heavy
unbalanced discharge, hopefully the balancer helps to balance during the charging process.
We have talked about building a balancer for many years now but it would have to be very
inexpensive to be a viable product.  There are some already out there I believe.  They're
not very powerful though as I remember.

boB

Thank you boB, I really was more interested in the first part of the comment :

"Multiple batteries in series is pretty hard to keep in balance especially if the string is tapped for lower voltage loads."

- It sounds like this " Multiple batteries in series is pretty hard to keep in balance" relates to tapped loads and not necessarily a string of cells or batteries to build voltage for loading and charging.  Am I correct?

A "balancer" would be awesome for people like me that have unbalanced ( A/H ratings that is ) battery groups to build a higher voltage array.  What I mean is, I have a ( all at 6hr load ) 1000ah 24v bank, a 935ah 24v bank and at times and a 1100ah 24v bank to build a 72v nominal system.  I know this is not ideal, but i gotta ask if a " balancer " could help folks like me?  Just maybe then the cost may be less of an issue.

[boB]

I probably should not have said that series strings are hard to keep balanced...   It's done all the time just fine.

But yeah, you still want to keep careful watch over time of the balancing for battery life.

One way is battery temperature.  I find that especially with AGM batteries, when they get unbalanced,
one or more batteries in the string will be hotter than the others.  I have used my hand to find the hot
ones before but voltage balance is probably better.

AGMs... They plump when you cook 'em !

(Sort of like the hot dogs)

boB

[boB]

Instead of tapping my 24 volt bank for the ham gear I went with a 24 to 12 volt converter. $100 well spent with less fussing with the batteries.

I am curious which one you use.   I know of Solar Converters for one.

boB

[Watt]

One way is battery temperature.  I find that especially with AGM batteries, when they get unbalanced,
one or more batteries in the string will be hotter than the others.  I have used my hand to find the hot
ones before but voltage balance is probably better.

I believe you are exactly right with the above.  I began noticing more balance problems with my decision to bring one of my weaker arrays up in SG.  I failed to watch the temperature of that one group as I began " balancing " it with the others.  As the batteries temperatures came up, I lost control quick.  I was able to finally realize the problem and eventually cooled the set with water.  That scheme would have been better had I monitored all the batteries temperatures. 

boB, That " Balancer " would be a great asset with enough bells and whistles to justify it.  It's all about buying something to let us be as lazy as possible.  J/k but I like that idea with multiple temperature and voltage monitor capabilities.

[boB]

If batteries get out of balance, I place them in parallel or just charge them individually at the same voltage which usually
gets them back on track.

The battery balancer would be a great thing to have.  It's had a lot of thought but no time to really
persue it.  Some day...  Hopefully sooner than later.

boB

[Watt]

If batteries get out of balance, I place them in parallel or just charge them individually at the same voltage which usually
gets them back on track.

The battery balancer would be a great thing to have.  It's had a lot of thought but no time to really
persue it.  Some day...  Hopefully sooner than later.

boB

That's what did it.  The ambient temperature was already hot when I started and.....   

I'll leave the " balancer " alone. 

Thanks boB.

[bob g]

i agree with boB about the series string issues with agm's and not to ever centertap the string for anything, ever!

i did it once on a 24volt string of agms, 4x6volts, tapped 12volts off for a temporary test and got distracted, called away and left the load attached..took me over a week of charge/drain/charge/equalize carefully, wash rinse repeat to get the pair back into shape,,, i didn't think i ever would get that done..

the way it was, even after a few recovery cycles i would still get a .3-.5 volt difference between the battery halves of the bank, the untapped top half would keep going well over 7.8 volts while the lower
would barely make 6.2 and the charger would then taper off.  7.8 volts on the upper batteries really makes a lot of heat, swells them up and is generally a bad deal all together, of course the 6.2 volts on the lower half batteries means they are not getting to even half charge which over time only gets worse in a hurry.

my next string will have a plus one strategy, meaning i will have one spare battery that gets rotated through the string, the spare can be monitored, charged and equalized if necessary to keep it into shape, and then swapped for a weak sister regularly.

i did the same as maryalana, i went to ebay and bought a 24/12 dc/dc converter, that allows me to have 6amps of 12volts for testing if needed. i also bought a 48/12 converter for when i am testing with a 48volt string... i think i paid about 20 bucks each for them, used surplus units,,, they seem to work fine and i suspect will give good service as long as i don't overload them, although i don't think the efficiency is as good as some of the higher dollar offerings. this i don't know for sure as i have not tested watts in vs watts out yet on either of them.

as for the series vs parallel argument, i suppose there are reasons why each is preferable under differing conditions.  as long as one is keeping a periodic eye on the battery conditions, water levels and specific gravity of each cell, either can be made to work out just fine.

bob g

[Volvo farmer]

You know, I didn't even consider that Chris' high current requirements might be a good reason to prefer parallel over series. With modern inverters though, is it really that important to keep the bus voltage high? I think my Outback is set somewhere in the mid 21 volt range for LVD.  With MPPT wind controllers, he doesn't need to keep the bank voltage high to keep his turbines operating in the sweet spot either.

Maybe the things I have read and heard are wrong, and maybe I don't understand the situation fully. However, it made sense to me at the time that if one string of parallel batteries reaches the target voltage while being charged, the current is limited to the whole bank, and some of the parallel strings' cells never get up to 1.275. So eventually, some strings begin to take more of the load and others become lazy. The SG begins to drift further and further away and it gets real hard to equalize the bank because the healthy strings achieve their target voltage more quickly, and you can never get enough current into the other strings to bring the SG up.

For me, 144 cells to check the water and SG on sounds like a real chore, and 48 + connections to check for tightness and corrosion every month or two? Not my idea of fun.

However, if it works, that's all that is important, and no amount of theorizing about it will change the fact that it works.  I would be very interested to see how this arrangement plays out in the next several years as these batteries age.

[ChrisOlson]

You said going on third winter but one of the posted thread reads as the batteries are new as of ( April 2011 ).

Well, I guess I considered that we put them in at the end of winter 2011, they went thru last winter, and now are entering their third winter (2012/2013).

I'm being really careful with these batteries to make sure they stay healthy because they cost us almost $10,000.  I became very alarmed in the initial stages of when we first got them because it didn't take long for them to get out of whack.  I've tried various schemes and the way I have them now seems to work the best.

Plus I have better equipment - my Classic controllers on both wind and solar are taking excellent care of them and charging them properly day after day, compared to what I used to have.  One of the things in the Classic that really helps is using what is called "Waste Not Hi" mode for "dumping" power.  After I got that tweaked it insures that the battery bank charging comes first and at the same time maximizes the output of of my wind and solar by keeping them performing at maximum possible output for heating our water.  It does not compromise proper bulk and absorb charging, and does not use exotic things like PWM, which is what I like about it.

And the auto gen start system we have now prevents them from ever being cycled too deeply, which also helps.

So perhaps I'm being overly cautious because of the cost of these batteries.  And they do have a 7 year warranty (pro-rated), but I still want them to last at least 10 years for us.  I'm happy at this point because normally batteries start to go downhill as soon as they are put into service, and these still load test with the identical specs of new ones after roughly 18 months in service.  And we work our batteries hard with our high-output system at times, many times pulling 300-400 amps from the bank.
--
Chris

[ChrisOlson]

Maybe the things I have read and heard are wrong, and maybe I don't understand the situation fully. However, it made sense to me at the time that if one string of parallel batteries reaches the target voltage while being charged, the current is limited to the whole bank, and some of the parallel strings' cells never get up to 1.275. So eventually, some strings begin to take more of the load and others become lazy.

VF, I think what boB mentioned about batteries connected parallel having to be at the same voltage is what makes this setup work well for me.  All 12 batteries in each string have to be at the same voltage - except under extreme load, possibly due to interconnect resistance, some might vary slightly for a short time.  But they still have to even out because that's the nature of the parallel connection scheme.

Having just the one series connection makes it simpler because I only have to monitor two banks, and if those two banks are the same I don't have to worry about any of the 24 batteries being different on charging voltage.

Indeed it is a chore to service them.  But I think any large battery bank is going to be a chore no matter what you do.  To get the amps required for our high power system would still take parallel banks of batteries, even if we used 2V cells.  Keeping the voltage at the bus up is VERY important to prevent inverter kick-out at full load.  Our inverters are rated at 25.2 volt nominal at full load.  They have to be de-rated if the voltage at the inverter studs is below that.  They will handle down to 22.0 volts with no problem, but they will not put out full power at 22.0.

And we run them at full power on a regular basis, depending on what my wife has going in the house, or I have going in the shop.  It is usually for a short time because our inverters have automatic load sharing where they bring the generator online to help out with heavy loads and the generator and inverters both supply power to run the loads.  But they have to be able to carry those loads because it takes up to 2 minutes to get the generator started and warmed up before they can use gen power for things like the clothes dryer or her electric range, or sometimes my welder, milling machine or lathe in the shop.
--
Chris

[Watt]

Maybe the things I have read and heard are wrong, and maybe I don't understand the situation fully. However, it made sense to me at the time that if one string of parallel batteries reaches the target voltage while being charged, the current is limited to the whole bank, and some of the parallel strings' cells never get up to 1.275. So eventually, some strings begin to take more of the load and others become lazy.

VF, I think what boB mentioned about batteries connected parallel having to be at the same voltage is what makes this setup work well for me.  All 12 batteries in each string have to be at the same voltage - except under extreme load, possibly due to interconnect resistance, some might vary slightly for a short time.  But they still have to even out because that's the nature of the parallel connection scheme.

Having just the one series connection makes it simpler because I only have to monitor two banks, and if those two banks are the same I don't have to worry about any of the 24 batteries being different on charging voltage.

Indeed it is a chore to service them.  But I think any large battery bank is going to be a chore no matter what you do.  To get the amps required for our high power system would still take parallel banks of batteries, even if we used 2V cells.  Keeping the voltage at the bus up is VERY important to prevent inverter kick-out at full load.  Our inverters are rated at 25.2 volt nominal at full load.  They have to be de-rated if the voltage at the inverter studs is below that.  They will handle down to 22.0 volts with no problem, but they will not put out full power at 22.0.

And we run them at full power on a regular basis, depending on what my wife has going in the house, or I have going in the shop.  It is usually for a short time because our inverters have automatic load sharing where they bring the generator online to help out with heavy loads and the generator and inverters both supply power to run the loads.  But they have to be able to carry those loads because it takes up to 2 minutes to get the generator started and warmed up before they can use gen power for things like the clothes dryer or her electric range, or sometimes my welder, milling machine or lathe in the shop.
--
Chris

Chris

I would like to be a fly on the wall as this system progresses.  You have so darn many batteries in parallel your batteries can't possibly see the same voltages ( so I guess ).  Anyway, Have you tried the rated inverter load and put a voltmeter on each battery to confirm you are correct with the wiring and have proper connection resistance? I have yet to see a picture of the batteries and their wiring connections so I still have my doubts as to exactly how they are wired.  I like the meters and in time, I too may trust them. 

Also, that argument regarding parallel strings would have to hold true whether the batteries are 6 volt, 12 volt, 24 volt, 48 volt etc....  Just because your batteries are in one package ( 12v ) makes them no different ( with proper wiring ) than a 24v series connected set of 2v cells. 

I don't believe boB meant literally any parallel connection, only a correct parallel connection. An improperly wired paralleled 12v set of batteries will never get an equal charge or load in a dynamic system.  It's the voltage at each connection considering those dynamics which charge and discharge a battery one at a time or all at the same time. 

I do have a problem with your setup already.  This is: why did your one battery get such a higher voltage than the others?  Proof is with the amount of water those cells took compared to the others.  Also, the amount of gassing these batteries are doing worry me as well - amount of water required for service.  I should not be concerned but, you have addressed your concern about the care due to their cost. 

[ChrisOlson]

I do have a problem with your setup already.  This is: why did your one battery get such a higher voltage than the others?  Proof is with the amount of water those cells took compared to the others.  Also, the amount of gassing these batteries are doing worry me as well - amount of water required for service.  I should not be concerned but, you have addressed your concern about the care due to their cost.

I suspect that one battery didn't get filled all way up the last time I had watered them, so it started out a little low on water level compared to the others.  Those batteries are hard to see where the water level should be because they don't have a transparent case.  And I tend to underfill the cells rather than overfill, because the few times I overfilled them I had acid bubbling out when they got warm and it was a mess and took a bunch of baking soda to clean it up.

I got Rolls batteries and they do not do well with low charging voltages.  So they tend to gas more than a Trojan I think.  In the really hot weather the battery temperature got well up over 110 degrees and I don't think they got below 100 degrees for most of July.  Add to that that we had day after day of bright sunny weather and they got bulk/absorbed every single day.  The temperature compensation had the absorb down to around 28.2 or so, but they still went thru a LOT of water.

Let me put it this way - my batteries are not going to die from being sulfated, and they got the plates in em to handle being bubbled all the time.  Just have to keep water in em.   
--
Chris

[Mary B]

Went with a converter from Samlex http://www.altestore.com/store/DC-to-DC-Voltage-Converters/Samlex-30-Amp-24-Volt-12-Volt-DC-DC-Converter/p9651/ only complaint is the fan runs continuous. I need to put in a disconnect switch.

[Watt]

I do have a problem with your setup already.  This is: why did your one battery get such a higher voltage than the others?  Proof is with the amount of water those cells took compared to the others.  Also, the amount of gassing these batteries are doing worry me as well - amount of water required for service.  I should not be concerned but, you have addressed your concern about the care due to their cost.

I suspect that one battery didn't get filled all way up the last time I had watered them, so it started out a little low on water level compared to the others.  Those batteries are hard to see where the water level should be because they don't have a transparent case.  And I tend to underfill the cells rather than overfill, because the few times I overfilled them I had acid bubbling out when they got warm and it was a mess and took a bunch of baking soda to clean it up.

I got Rolls batteries and they do not do well with low charging voltages.  So they tend to gas more than a Trojan I think.  In the really hot weather the battery temperature got well up over 110 degrees and I don't think they got below 100 degrees for most of July.  Add to that that we had day after day of bright sunny weather and they got bulk/absorbed every single day.  The temperature compensation had the absorb down to around 28.2 or so, but they still went thru a LOT of water.

Let me put it this way - my batteries are not going to die from being sulfated, and they got the plates in em to handle being bubbled all the time.  Just have to keep water in em.   
--
Chris

Time will tell whether what you are doing is right or not Chris.  I really do hope you let one battery slip by the fill procedure.  Those plates are not any thicker than traction battery plates and even traction battery plates don't fair well in high temperatures.  That gassing also causes battery temps to rise.  The gassing and the high temps are not good even for Rolls sets.  I wonder if you should consider lowering the voltages a bit for the summer time to help compensate for the added temps with your charge scheme?  Just wondering.

[ChrisOlson]

I wonder if you should consider lowering the voltages a bit for the summer time to help compensate for the added temps with your charge scheme?  Just wondering.

I don't know for sure.  When things are more normal as far as temperatures, they seem be able to get thru absorb stage at 30.0 volts usually pretty quick.  In the hot weather the temperature compensation had them down to around 28.2 volts for absorb and it seemed to hold them there almost every day until the 3 hour absorb timer expired before it dropped them into float because they just kept pulling too many amps.

Now that we're back in cooler weather and the batteries are running around 70 degrees they are getting absorbed at 30.0 again.  I got the timer set in the Classic for minimum 1 hour absorb and maximum 3 hours, with the ending amps at 2% of the ah capacity of the bank, or 48 amps.  Today, for instance, the Classic dropped them into float immediately after the one hour minimum had been reached because they were only pulling about 35 amps after one hour.

For some reason they just kept pulling over 48 amps during absorb in the hot weather and the Classic would boil them at 28.2 volts for the full three hours.  I don't think they ever got fully charged - they couldn't have because they were still pulling too many amps at the temperature compensated voltage.

I even had a fan blowing on them and that didn't do any good when the fan is blowing 100-105 degree air on the batteries.  It got so hot in July that the shallower lakes in some places got hot and killed all the fish around here.  I've never seen anything like it, and hope to never see it again.  Now that we're down to more normal temperatures those batteries will go for 3 months without requiring any water.  So, like I say, I don't know.  I can only assume that the batteries didn't like the hot weather back in July any more than I did, or anything else did.  But what do you do when it's over 100 degrees day after day?  I didn't own a big enough AC unit to cool off two tons of lead that was hot-soaked to 110 degrees.
--
Chris

[bob g]

Chris

when it is 100 degrees plus during the day, what does the ambient outside air drop to at night?  and what is the average relative humidity?

the reason i am asking is, i too live in a hot climate, and am concerned about heat rejection and via research and testing have decided to do the following

the battery shed will have a thick well insulated concrete slab for the batteries to rest on, in the slab i plan on a water loop. during the overnight hours i plan on using a mini cooling tower to take the heat out of that slab, leaving a cold sink for the batteries to reject heat to during the day.  of course the shed will be very well insulated and positioned with an eye toward natural shading.

with med/low humidity a cooling tower can cool water to ~10degree's below ambient, so on a night that might get down to 75 degree's i think i can get the slab down to 65 degree's before morning.  using lots of concrete the slab can absorb a lot of heat from the batteries, and also keep the room well below outside temperatures during the heat of the day.

running the batteries at higher temperatures will increase their capacity, but also reduce their lifespan, conversely running them cold will decrease capacity and increase their lifespan... if you have an eye on longevity as your primary goal, it would seem that getting and keeping them cool is the way to go?

i bet the core temperatures of some of the batteries near the core of the stacks is well over 125 degree's F, and is very likely to dramatically shorten their lifespan.

my opinion only, based on talking to rolls/surrette and other flooded cell manufactures engineering departments, heat is your enemy.

bob g

[Watt]

I wonder if you should consider lowering the voltages a bit for the summer time to help compensate for the added temps with your charge scheme?  Just wondering.

I don't know for sure.  When things are more normal as far as temperatures, they seem be able to get thru absorb stage at 30.0 volts usually pretty quick.  In the hot weather the temperature compensation had them down to around 28.2 volts for absorb and it seemed to hold them there almost every day until the 3 hour absorb timer expired before it dropped them into float because they just kept pulling too many amps.

Now that we're back in cooler weather and the batteries are running around 70 degrees they are getting absorbed at 30.0 again.  I got the timer set in the Classic for minimum 1 hour absorb and maximum 3 hours, with the ending amps at 2% of the ah capacity of the bank, or 48 amps.  Today, for instance, the Classic dropped them into float immediately after the one hour minimum had been reached because they were only pulling about 35 amps after one hour.

For some reason they just kept pulling over 48 amps during absorb in the hot weather and the Classic would boil them at 28.2 volts for the full three hours.  I don't think they ever got fully charged - they couldn't have because they were still pulling too many amps at the temperature compensated voltage.

I even had a fan blowing on them and that didn't do any good when the fan is blowing 100-105 degree air on the batteries.  It got so hot in July that the shallower lakes in some places got hot and killed all the fish around here.  I've never seen anything like it, and hope to never see it again.  Now that we're down to more normal temperatures those batteries will go for 3 months without requiring any water.  So, like I say, I don't know.  I can only assume that the batteries didn't like the hot weather back in July any more than I did, or anything else did.  But what do you do when it's over 100 degrees day after day?  I didn't own a big enough AC unit to cool off two tons of lead that was hot-soaked to 110 degrees.
--
Chris

Do like the doctors do us when we are too hot, pack them batteries in ice.  As far as temperatures go, we see those temperatures and more around here - daily. 


As far as absorb goes, I wonder if you have been watching the SG of the set during the hot weather.  Temperature compensated, that cycles' SG may have been met and you may have been burning off that amperage.  With that many batteries, 35amps and 30v+ is nothing and certainly not much current flow at even less than 2% C rate.  In float, you could easily use that sorta current.  I'd be looking more at the SG of the set to determine absorb, not depend on the Classic.  I'm not saying the Classic is not the bee's knees, I'm just saying it does as it's told. 

[Watt]

Chris

when it is 100 degrees plus during the day, what does the ambient outside air drop to at night?  and what is the average relative humidity?

the reason i am asking is, i too live in a hot climate, and am concerned about heat rejection and via research and testing have decided to do the following

the battery shed will have a thick well insulated concrete slab for the batteries to rest on, in the slab i plan on a water loop. during the overnight hours i plan on using a mini cooling tower to take the heat out of that slab, leaving a cold sink for the batteries to reject heat to during the day.  of course the shed will be very well insulated and positioned with an eye toward natural shading.

with med/low humidity a cooling tower can cool water to ~10degree's below ambient, so on a night that might get down to 75 degree's i think i can get the slab down to 65 degree's before morning.  using lots of concrete the slab can absorb a lot of heat from the batteries, and also keep the room well below outside temperatures during the heat of the day.

running the batteries at higher temperatures will increase their capacity, but also reduce their lifespan, conversely running them cold will decrease capacity and increase their lifespan... if you have an eye on longevity as your primary goal, it would seem that getting and keeping them cool is the way to go?

i bet the core temperatures of some of the batteries near the core of the stacks is well over 125 degree's F, and is very likely to dramatically shorten their lifespan.

my opinion only, based on talking to rolls/surrette and other flooded cell manufactures engineering departments, heat is your enemy.

bob g

I like the idea Bob but, heat rises and not much heat will be rejected through the floor as the cases and battery tops will reject most in the shed interior.  Heating a room with coiled tubing in the slab is by far more efficient than cooling a room.  Just sayin'.

[ChrisOlson]

when it is 100 degrees plus during the day, what does the ambient outside air drop to at night?  and what is the average relative humidity?

I don't remember the humidity - mostly above 85% I think.  The night time temps were getting down to 90-95 or so.  I think they said July set an all-time record for heat, pretty much all across the country.  According to the Weather Service:

The heat for the month beat out the record heat experienced during the Dust Bowl era back in July 1936.  Persistent heat across much of the continental U.S. resulted in July 2012 being the warmest single month on record since official records began in 1895
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Chris

[Frank S]

Chris I know excavation can be expensive NO not can be IS expensive.
 Over here Hospitals and other places that absolutely must maintain 100% instant un-interrupt-able power  place their bank of cells as deep as 12 to 15 meters in the ground in meter thick concrete walled vaults
 The new Cardiac hospital they are building will have a half a million dollar bank of cells it is estimated that that will be a 800% over capacity reserve so 80% of the cells will be in their dry as shipped still packaged long term storage mode. Its nice to have more money than you can afford to spend

[ChrisOlson]

Do like the doctors do us when we are too hot, pack them batteries in ice.

Basically, if we took all of our food out of the freezer and just left it rot so we could use the whole freezer to make ice for the batteries, we could not make enough ice to cool 2 tons worth of batteries.  So what we'd end up with hot batteries, a flooded utility room, and rotten food.
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Chris

[ChrisOlson]

Chris I know excavation can be expensive NO not can be IS expensive.

Yeah, but putting those batteries in anyplace where you can't handle them with a forklift or skid steer is a disaster.  They are too heavy to have in an underground vault.  And the inverters can not live in there - they would have to be in a place that is not damp with acid fumes coming out of batteries.  That is why I have the batteries in separate cases that are vented to the outside - so it doesn't destroy my other equipment.

I'm going to consider that July was not normal, and they just needed water checked more often.  Plus we had a window AC unit going around the clock to keep the house around 90 degrees inside, and that took a lot of power too.  Even with our power system, we can not run a central AC unit.
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Chris

[bob g]

i agree it is less efficient to suck heat down but remember the cases have a very intimate contact with the case to concrete interface and from the electrolyte to the case... this close contact will transfer heat much more readily than from the case to the air.  heat seems to have an affinity towards travel to the colder region, even if it has to move downwards.

heat pipes are a good example of counterflow principles.

not optimal, but its amazing how well it works in practice

i suppose it might also be something where a wall could also be cast in concrete and also cooled? maybe that would help to create and maintain an air turnover within the room?

just something to consider, and maybe something to research a bit further?

bob g

[vtpeaknik]

Regarding hot batteries sitting on cool concrete:  I remember reading that putting batteries on concrete is bad for them.  I pooh-poohed that as some sort of "old wives tale".  But then I read somewhere that the reason it's a problem is because it causes a temperature gradient inside the battery.  Warmer far away from the floor.  You want your charge controller to adjust the voltage for the temperature.  But which temperature?  If the temperature inside the battery is not uniform, some parts of the battery are experiencing the wrong voltage.

[Watt]

Do like the doctors do us when we are too hot, pack them batteries in ice.

Basically, if we took all of our food out of the freezer and just left it rot so we could use the whole freezer to make ice for the batteries, we could not make enough ice to cool 2 tons worth of batteries.  So what we'd end up with hot batteries, a flooded utility room, and rotten food.
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Chris

Or, do that.  It's easier to buy a few bags of ice.  But, if you like rotten food....   Being an engineer, I would never have guessed you would accept such a disaster in your utility room.  Surely you could think/produce a better option for your batteries. 

[bob g]

with the charging capacity Chris has i would expect that the electrolyte will be rolling internally, leaving it all well mixed and no real temperature gradient. this might be a problem with large battery banks and insufficiently sized charging sources, whether or not you are sitting on the floor.

far better to have to worry about too cold, no damage can occur provide you have enough charging capacity to stir the electrolyte, if you are gassing and bubbling you are mixing adequately well, than to operate a battery bank at elevated temperature which is proven to dramatically reduce their lifespan.

the old wives tale was based on the old tar top batteries, wherein the cases would get a coating of acid and dust, being damp they would drain away charge sitting on the concrete, and on cold mornings with very  cold concrete the batteries capacity was so reduced so as to appear like they were drained by sitting on the concrete. the reality is there were other things in play that most folks didn't realize.

misapplication of cause and effect

bob g